Method of producing a wheel speed sensor and the corresponding sensor

ABSTRACT

Manufacture of a speed sensor, including a cable ( 15 ) containing electrical wires for connection between the sensor and a data processing unit, pins joined to the wires and to connection blades of a member for detecting the rotation speed of the wheel of the vehicle, a first molded plastic casing portion ( 3 ), having a shaft ( 13 ) molded around one end of the wires of the cable, and a cavity in which the pins and the detection member are placed, the pins being mutually separated and the wires being mutually separated at the point of their stripped end, and the detection member being held in place in the cavity of the first casing portion by retaining lugs made of one piece with this first casing portion, and a second casing portion ( 5 ) including a part that isolates the pins and the detection member from the outside.

The invention relates to the manufacture of a speed sensor for thewheels (or one wheel) of a vehicle, in particular a motor vehicle.

Typically, it is important in certain safety systems (in particular forantiskid or antilocking when braking) to know the rotation speed of thewheels of the vehicle.

To do this, it is known to use a sensor provided with a detection memberthat detects the rotation speed of the wheels of this vehicle. Thesensor is connected to a means for processing the data acquired, so asto use this data within the safety system.

In this context, the invention relates more particularly to a processfor manufacturing such a sensor and to the sensor itself.

A typical sensor of the prior art comprises a detection member asmentioned above (usually comprising an electronic circuit and electricalconnection blades) and a protective casing. In the casing, theconnection blades are connected to a stripped end of the electricalwires of a cable via pins. The casing is designed to be fastened ontothe vehicle. The detection member may be of electromagnetic type and isthen designed to work typically in conjunction with facing striations orfacing teeth formed on the wheel of the vehicle when the sensor iscombined with a ferromagnetic target or a succession of North and Southpoles in the case of a magnetic target.

One problem that the invention aims to solve is to simplify theconditions under which such sensors are manufactured, so as to reducescrap and, if possible, to shorten the cycle times, and also to reducethe overall cost of the sensor.

To manufacture the sensor, one solution proposed in the inventionconsists of the following:

-   -   a cable is placed in a mold, said cable comprising electrical        wires provided with pins for connection between the sensor and a        means of processing the data acquired by this sensor, and a        separator is interposed locally between said wires and/or their        pins, avoiding any electrical contact between these wires and        these pins at least during the subsequent molding step;    -   a first casing portion is molded around one end of the cable and        around the pins joined to the wires,        -   leaving open at least one cavity in which at least one            portion of said pins is located, these being intended to            ensure electrical contact between the wires and connection            blades with which a member for detecting the rotation speed            of the wheels of the vehicle is provided,        -   reserving a region in the cavity for housing the detection            member and its blades, and        -   providing, on at least one portion of the periphery of this            cavity, a rim lined on the inside, at least locally, by a            wall, in order to define a fusible region;    -   the detection member of the sensor is placed at that point in        the region that is reserved for it in the cavity, its blades        then preferably being located in immediate proximity to the        pins;    -   the pins and the blades of the detection member are welded or        soldered to each other in the cavity, this detection member        being held in place with respect to the casing by retention lugs        that are molded with said first casing portion; and    -   the cavity is closed, facing the pins and the detection member,        by means of a second casing portion fusion-bonded at the point        of the fusible region.

In this way, the risks of a short circuit during manufacture of thecasing and during imprisonment of the electrical connectors (wires,pins, etc.) are limited, the sealing conditions are favored (especiallyby molding the first casing portion around one end of the cable), andthere is overall a reduction in the number of operations and/or themanufacturing cycle time.

One important feature also relates to holding the detection member inplace with respect to the casing.

According to one feature of the invention, this retention isadvantageously obtained by means of lugs which extend toward theinterior of the cavity and are molded during the step of molding saidfirst casing portion, the steps of placing the detection member in thecavity and of soldering it therein including a step of engaging saiddetection member under and/or between the lugs in order to hold it inplace.

This therefore avoids a rework operation after the first casing portionhas been molded.

Another feature of the invention favors the soldering of the connectionblades of the detection member to the pins.

For this purpose, it is recommended that the step of molding the firstcasing portion around the wires and the pins comprise the reservation ofan opening that communicates with the cavity, in a localized region ofthe pins, in order to allow electrical soldering between the blades ofthe detection member and the pins, by means of electrodes placed oneither side of the pins and the blades.

This increases the overall reliability of the sensor.

Another feature of the invention the sealing conditions in the cavity ofthe casing to be further improved.

To do this, it is recommended that the step of closing this first casingportion comprise the localized overmolding of the first casing portionwith the second, which closes the cavity forming a liquid-tight anddust-tight seal, at the place of a single lip which defines said fusibleregion that is made to fuse during the overmolding and which extendsaround the periphery of the cavity, over a height and a thickness thatare less than those of the rim that surrounds it.

As already indicated above, the invention also relates to the speedsensor itself.

One important feature relating to this is that its first plastic casingportion comprises a shaft molded around one end of the wires of thecable, in order to intimately surround them so as to form a liquid-tightand dust-tight seal, and a cavity in which the pins and the detectionmember are placed, the pins being mutually separated and the wires beingmutually separated at the point of their stripped end, and the detectionmember being held in place in said cavity of the first casing portion byretaining lugs made as one piece with this first casing portion.

With regard to sealing the reception cavity, especially the detectionmember, it is also recommended that said connection lip, that can meltmore rapidly than the rim, and is therefore fusion-bondable with thesecond casing portion, be formed by a single wall over the entireperimeter of the cavity.

Yet another feature of the invention has the purpose of limiting therisks of the cable (which is cylindrical) rotating during the operationof manufacturing the sensor, which rotation would result in an incorrectassembly.

One solution proposed is that the shaft of the first casing portion has,on the outside, at least one parallelepipedal (typically rectangular orsquare) flange.

An even more detailed description of the invention will now be providedwith reference to the appended drawings, in which:

FIG. 1 is a ¾ top perspective view of the sensor ready to be fastenedonto the vehicle that is intended to be equipped therewith;

FIG. 2 is also a perspective view “from above” of a first step in themanufacture of the sensor (the detection member and the second casingportion not being present);

FIG. 3 also shows, in perspective “from above”, the sensor of FIG. 2with the detection member installed;

FIG. 4 shows the pins, the wires and the cable for transmitting the dataacquired by the detection member, before they are embedded by theplastic of the first casing portion, which is molded around them; and

FIG. 5 is a sectional view on the line V-V of FIG. 2.

FIG. 1 shows an illustrative example of a sensor 1 according to theinvention, in its fully assembled state.

The sensor 1 comprises a first casing portion 3, which may be moreclearly seen in FIGS. 2 and 3, and a second casing portion 5.

The second casing portion is a plastic sealing part overmolded onto thefirst casing portion 3, especially in order to seal off a cavity 7 ofthe portion 3, and also the well 9 of the same portion 3.

The sealing part 5 is furthermore equipped with a screw 11 for fasteningto a wall of the vehicle.

The part 5 ensures that the parts contained inside the cavity 7 aresealed with respect to liquids and dust.

In its molded state shown in FIG. 3, the first casing portion 3 takesthe form of a one-piece part made of a meltable plastic and has a shaft13 that may also be seen in FIG. 1, from which emerges at the rear(again in a liquid-tight and dust-tight manner) a cable 15 whoseelectrical wires are connected, on one side, to a data processing means16, such as an electronic calculator (FIG. 4), and, on the other side,to pins 17 a, 17 b that are electrically connected to the blades 19 a,19 b of a detection member 21, known per se.

The detection member 21 comprises an electronic board 22 designed todetect, particularly by electromagnetism, the rotation speed of a wheelof a vehicle, for example in conjunction with striations formed facingit on this wheel.

As shown in FIGS. 2 and 3, the shaft 13 extends from the rear end 3 a ofthe first casing portion 3 as far as a kind of box 23, which is openhere and defines, on the inside, the cavity 7 in which at least oneportion of the pins 17 a, 17 b and the detection member 21 are housed.

Provided at one point on the shaft 13 is the transverse well 9 throughwhich the electrical wires (in this case two wires) of the cable 15pass. At this point, the wires are not stripped.

The production of the part illustrated in FIG. 3 is carried out asfollows, with a first step consisting as illustrated in FIG. 2.

As illustrated in FIG. 4, the terminal end of the cable 15, and inparticular the two wires 25 a, 25 b that emerge from its jacket 27, andthe two pins 17 a, 17 b, to which a stripped end 25′a, 25′b of theelectrical wires is already connected, are placed in a mold.

To avoid short circuits between the wires 25 a, 25 b, and between thepins 17 a, 17 b, it is recommended to provide, in the mold, a separatingwall (not shown). Optionally, this wall can be moved, that is to say itis retractable. Another already known solution could consist in theaddition of a plastic separator attached or molded between the wiresand/or between the pins, as shown schematically at 26 in FIG. 4.

Once the assembly shown in FIG. 4 has been correctly positioned and heldin place in the molding cavity, the plastic needed for molding the firstcasing portion 3 shown in FIG. 2 is supplied.

Typically, the molding will be carried out by injecting pressurizedplastic into the molding cavity.

It may be noted that this part has, near the rear end 3 a, one or moreparallelepipedal flanges, such as 27 and 29, which can be used as anantirotation and/or stop device for subsequently placing, in the correctmanner, the sensor in the assembly line, in particular when fastening itto the vehicle.

The transverse well 9 that passes right through the shaft 13 allows theoperator to see the passage of the wires 25 a, 25 b and to check thatthey are correctly positioned both with respect to each other and withrespect to the pins, which are at least partly visible inside the cavity7, and are parallel to each other.

In this case, the two-stage aspect of the cavity may be noted: the pinsare located at a different height from that of the front region 31reserved, opposite the pins, for housing the electronic board 22, theblades 19 a, 19 b of which have here a curved shape in order to “take upthe difference” in level of the pins to which they have to beelectrically connected (see FIG. 3).

It should also be noted, in FIGS. 2 and 3, that there is, across thebottom (which is moreover solid) of the cavity 7, facing the pins, anorifice 32 passing through this bottom, the utility of which will beexplained below.

It should also be noted that the entire perimeter of the box 23 has anupright wall 33 advantageously lined on the inside by a thinner fusiblelip 35.

Preferably, this lip is formed by a single wall that is continuous overmost (and preferably all) of the perimeter of the cavity, a shortdistance from the outer rim 33, as may be seen in the cross section inFIG. 5.

This lip is advantageously made of the same material as the rim and,more generally, as the rest of the first casing portion 3.

In FIG. 5, the height h and the thickness e of the lip 35 are less thanthose of the outer rim 33 which thus protects the lip, the lattertapering down toward its free end in order to favor rapid melting. Inthis case, it is also a beveled lip.

It should also be noted that the regions where the first casing portion3 is manipulated are preferably remote from the lip such as for exampleat the place of the lugs 37, 39 and 41 that may be used as stops forguaranteeing the precise positioning of said casing portion 3 in theovermolding mold and/or of the sensor 1 in the assembly line when it hasto be fastened to the vehicle.

In FIG. 2, the detection member, with its electronic board 22 and itsconnection blades 19 a, 19 b, has not yet been placed in the cavity 7.

However, it should be noted that, at the region 31, lugs (in this casetwo in number, namely 43 and 45) may already have been molded duringmolding of the first casing portion 3, under (or between) which lugs theboard 22 may be slipped and held in place pressed into the casing.

Thus, once the first casing portion 3 has been molded as illustrated inFIG. 2, the board 22, with its connection blades 19 a, 19 b, may be slidinto its housing, the free end of the connection blades facing (in thiscase above) the thinner end of the pins 17 a, 17 b.

It should be noted that the overlap part between the pins and theconnection blades nevertheless lies facing the orifice 32 in the box 23.

This particular feature makes it possible to place, above the cavity 7,a first soldering electrode 46 located facing this overlap part betweenthe pins and the connection blades, the second welding electrode 48being located in the orifice 32, so that an electrical discharge betweenthese electrodes allows each pin and each blade to be electricallyconnected together.

To hold the blades in place, a plastic insert 47 may be provided, whichis held against the casing portion 3 in a reserved housing 49 (see FIG.2), after molding.

Rather than fitting the detector board 22 under the molded lugs 43, 45and retaining them there, it will be possible to choose to place theboard in its housing 31 and then to carry out a subsequent operation inorder to fasten it to the casing, in particular by snap-riveting.

Once the part is in its state as shown in FIG. 3, there remains only toclose the cavity 7 and the well 9, by means of the sealing part 5.

To do this, it is recommended to place the whole assembly illustrated inFIG. 3 in an overmolding mold in order to inject the part 5.

During this operation, the cavity 7 will in particular be able to besealed off by means of the fusible lip 35, the melting of which togetherwith a corresponding portion (not shown) of the material of the part 5will entirely close off the cavity, most particularly if this lip 35extends continuously around the entire perimeter of the cavity.

The part 5 embeds the well 9, but leaves the positioning flanges 27, 29exposed.

1. A process for manufacturing a wheel speed sensor for a vehicle, whichcomprises: placing a cable (15) in a mold, said cable comprisingelectrical wires (25 a, 25 b) provided with pins (17 a, 17 b) forconnection between the sensor and a means of processing data acquired bysaid sensor, and interposing a separator (26) locally between said wiresand/or their pins, avoiding any electrical contact between these wiresand these pins at least during a subsequent molding step; molding afirst casing portion (3) around one end of the cable and around the pinsjoined to the wires, leaving open at least one cavity (7) in which atleast one portion of said pins is located, these being intended toensure electrical contact between the wires and connection blades (19 a,19 b) with which a detection member for detecting the rotation speed ofthe wheels of the vehicle is provided, reserving a region (31) in thecavity for housing the detection member and its blades (21; 22, 19 a, 19b), and providing, on at least one portion of the periphery of thiscavity, a rim (33) lined on the inside, at least locally, by a wall(35), in order to define a fusible region; placing the detection member(22) of the sensor at that point in the region (31) that is reserved forit in the cavity; welding or soldering the pins and the blades (19 a, 19b) of the detection member to each other in the cavity, said detectionmember being held in place with respect to the casing by retention lugs(43, 45) that are molded with said first casing portion; and closing thecavity, facing the pins and the detection member, with a second casingportion (5) fusion-bonded at the point of the fusible region (35). 2.The process as claimed in claim 1, characterized in that the detectionmember is held in place with respect to the casing by means of lugs (43,45) which extend toward the interior of the cavity (7) and are moldedduring the step of molding said first casing portion (3), the steps ofplacing the detection member (21) in the cavity and of soldering ittherein including a step of engaging said detection member under and/orbetween the lugs in order to hold it in place.
 3. The process as claimedin claim 1, characterized in that the step of molding said first casingportion (3) around the wires and the pins comprises the reservation ofan opening (32) that communicates with the cavity (7), in a localizedregion of said pins, in order to allow electrical soldering between theblades of the detection member and the pins, by means of electrodes (46,48) placed on either side of the pins and the blades.
 4. The process asclaimed in claim 1, characterized in that the step of closing said firstcasing portion (3) comprises the localized overmolding of the firstcasing portion with the second, which closes said cavity (7) forming aliquid-tight and dust-tight seal, at the place of a single lip (35)which defines said fusible region (5) that is made to fuse during theovermolding and which extends around the periphery of the cavity, over aheight and a thickness that are less than those of a rim (33) thatsurrounds it on the outside.
 5. A wheel speed sensor for a vehicle,comprising: a cable (15) containing electrical wires (25 a, 25 b) forconnection between the sensor and a means (16) of processing dataacquired by this sensor; pins (17 a, 17 b) joined to the wires and toconnection blades (19 a, 19 b) of a member (21) for detecting therotation speed of the wheel of the vehicle; a first molded plasticcasing portion (3), comprising a shaft (13) molded around one end of thewires of the cable, in order to intimately surround them so as to form aliquid-tight and dust-tight seal, and a cavity (7) in which the pins andthe detection member are placed, the pins being mutually separated andthe wires being mutually separated at the point of their stripped end,and the detection member being held in place in said cavity of the firstcasing portion by retaining lugs (43, 45) made as one piece with thisfirst casing portion; and a second casing portion (5) comprising a partthat isolates the pins and the detection member from the outside, so asto form a liquid-tight and dust-tight seal.
 6. The sensor as claimed inclaim 5, characterized in that the cavity (7) of the first casing partis bordered by a rim (33) lined internally, at least locally, by a wall(35) that can melt more rapidly than the rim, so as to constitute aconnection lip that is fusion-bondable with the second casing portion(5).
 7. The sensor as claimed in claim 6, characterized in that the lip(35) is thinner and lower than the rim (33) that surrounds it.
 8. Thesensor as claimed in claim 6, characterized in that the lip (35) isformed by a single wall extending over the entire perimeter of thecavity.
 9. The sensor as claimed in claim 6, characterized in that theshaft (13) of the first casing portion has, in the absence of the secondcasing portion, an open well (9) allowing the electrical wires of thecable crossing it to be seen.
 10. The sensor as claimed in claim 5,characterized in that the shaft (13) of the first casing portion has aparallelepipedal flange (27, 29) for preventing the cable from rotating.